SC 063 INSTRUCTION MANUAL
56-101-01200, Rev. D GEN. INFO.
September
/ 9 / 2010 Page 8 of 20
(1) Hard Iron:
This term is given to those parts of the Aircraft, which may be regarded
as permanent magnets; that is, parts in which the magnetism tends to remain the
same. The effect of hard iron can be determined with fair accuracy during a
Compass swing. By the use of other permanent magnets (compensating magnets)
near the Compass, it usually can be compensated for completely. Once such
compensation has been accurately made, it will remain effective so long as the
magnets do not alter their strength or position. If the compensation is not complete
and some error remains in the Compass, the error will alter as the Aircraft changes
magnetic latitude. For this reason, the accurate correction of the Aircraft’s
permanent magnetism is extremely important.
(2) Soft Iron: This term is given to those parts of the Aircraft which continuously change
their magnetism, depending on the influence of other magnets (such as earth) on
them. The soft iron magnetism will change the Compass deviation with the change
of magnetic latitude if it results from the presence of unsymmetrical, vertical soft iron
near the Compass. The compensation of an Aircraft for soft iron magnetism is so
complicated as to be impractical and should be performed only by an expert. It is
important, therefore, that the Compass location be such that there is no soft iron
near it.
(3) Electrical Magnetism: This term is given to the magnets (magnetic fields) which are
produced by a direct electrical current flowing through a wire. Since the direct
current, causing electrical magnetism, is liable to change frequently during a flight, it
is of the utmost importance that any single-pole wires carrying a direct current
should not pass anywhere near the Compass. If it is impossible to avoid this wiring,
then it is essential that the wiring be of the two-pole type. Experience has shown
that the use of single- pole electrical wiring near the Compass has such a serious
effect that it cannot be tolerated.
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